This invention relates generally to an apparatus for mixing air and fuel in a burner. More specifically, the geometry of the flow path of the air and fuel are made to result in maximum mixing of the fuel and air components. The air first passes through a set of fins providing some prerotation to the air before the fuel is admitted. Then the air and fuel mixture passes through another set of fins angled in a direction opposite that of the first set of fins to enhance mixing. Finally, the mixture is exposed to burning fuel, which ignites it.
To supply heat by combusting fuel, an oxidant is required. In a typical burner application such as those for steam generation, a hydrocarbon fuel is mixed with air and the mixture ignited. When mixing of the fuel and oxidant is complete prior to burning, combustion will be most efficient, resulting in the greatest heat output, uniform heating, and minimum incomplete combustion. If adequate mixing is not attained, the combustion will be less efficient, resulting in less heat output and a greater emission of pollutants, specifically carbon monoxide. xe2x80x9cHot spotsxe2x80x9d may also result.
The problem is compounded when the burner must be made to allow for variable fuel and air flow rates. Due to varying Reynolds number with changing flow rates, the turbulence intensity and the scales of the eddies are not the same throughout the operating region.
For the reasons given above as well as others, there is an obvious need for a burner that provides maximum mixing of fuel and air for combustion.
A purpose of this invention is to provide an apparatus for mixing gaseous fuel and air in a burner. It incorporates vanes with opposing slopes to enhance mass and momentum transfer associated with turbulent fluid flow. Turbulence is instrumental to obtaining rapid, complete mixing of dissimilar fluids.
The air entering the burner assembly is first given a prerotation by a first set of fins or vanes. After exiting this set of fins, the fuel is introduced radially, into the air through a series of orifices around the circumference of a collar. The two gases then enter another set of fins that are angled in the opposite direction from the first set that the air passed through. This change in rotation direction results in turbulent mixing which prepares the mixture for ignition and consequent complete combustion.
Another aspect of the burner assembly is a carefully sized, small pilot tube that carries combustion air from upstream of the fin assemblies to a xe2x80x9cTxe2x80x9d in which fuel is added to the air. From there, the mixture passes an ignitor to provide the threshold energy to initiate burning. This small amount of burning mixture enters the main air-fuel mixture downstream of the second set of fins and causes that mixture to combust.